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The virtual library.

Before the internet became fun, it was a tool for scientists. Astronomers would send correspondence and data to colleagues with electronic immediacy. Within the last two years the availability of information on the Internet has exploded. Today this globe-spanning network not only remains an important communication tool but also is an astronomical resource - one no longer limited to professional astronomers.

One valuable feature is the Astrophysics Data System (ADS), a NASA-funded project located at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. It was founded several years ago to provide access to scattered astronomical databases. At that time the World Wide Web (WWW) did not exist. My colleagues and I therefore developed our own system to offer several hundred astronomical catalogs and more than 100,000 abstracts (summaries of research papers with overviews of the observations and results).

As the popularity of the WWW grew, it became immediately obvious that it delivered most of what the "classic" ADS did. We therefore shifted our efforts to support WWW access, so the information would be freely available to anyone - including amateurs with a computer and modem.

This article outlines the ADS's abstract service, online articles, and catalog service; it also describes how to use each. The combination of services lets you search through the astronomical literature, read astronomical journals online, print articles for personal use, and search scores of astronomical databases. You can find the ADS at http://adswww.


The abstract service provides overviews of most astronomical literature since 1975. We currently have nearly a million abstracts and references in our database, including conference proceedings, technical reports, and Ph.D. theses. We also receive information directly from an increasing number of online astronomical journals.

The database is accessed by filling out a form linked to the WWW page Currently, we have three categories of abstracts online: astronomy and astrophysics, instrumentation, and physics and geophysics. The query form allows the user to specify search criteria based on author names, keywords, or words in the title or abstract; similarly, search filters and parameters for ranking the hits can be specified.

To illustrate the capabilities, let's make a test run. A recent hot topic concerns finding planets around other stars, so I executed a query for "detection of planetary systems around extrasolar stars." The right-hand screen at the top of the next page displays the results, featuring the most recent publications on this subject. The sixth reference is particularly interesting. It's to a talk presented at the June 1995 meeting of the American Astronomical Society by Geoffrey Marcy and Paul Butler reporting about their efforts in this quest. We now know that these two astronomers have since detected planets around relatively close-by stars (August issue, page 20). Further in the query results you'll find the abstract concerning their discoveries.

For each reference the search lists a bibliographic code, authors, title, publication date, and a score that rates how closely the result matches the query. Links to other available information include:

NASA/STI abstract (A): the core of the database.

Original author abstracts (O): summaries directly from the journal.

Full articles (F): bitmapped articles from several journals; these can be viewed on the computer or printed.

Data links (D): hypertext links to journal articles that have data available online.

Electronic journal (E): links to articles in the Astrophysical Journal Letters, now available on the WWW (February issue, page 13).

Author notes (N): author commentaries about their articles, such as clarifications, corrections, or even hyperlinks to other articles.

SIMBAD objects (S): the SIMBAD database, a service of the Astronomical Data Center in Strasbourg, France, lists an article's astronomical objects.

The abstract service can also be accessed via electronic mail. For instructions, send a message to with the word "help" in the message body, or view the information on the WWW at


Another facet of the ADS is the article service, which accesses a steadily increasing number of astronomical journals online. While you may hear about a discovery from the popular press, the primary sources for scientific findings are professional journals.

For example, a News Note in the March Sky & Telescope reports about "Quasars: Not Naked After All" (page 12). The text notes that the full report by the researchers - Kim K. McLeod and George H. Rieke - appears in the December 1, 1995, Astrophysical Journal Letters. We can call up this paper using the ADS by going to the WWW page and retrieving that issue's table of contents. A couple of pages down we find the authors' names on the article "Luminous Quasars in Luminous Early-Type Host Galaxies." Selecting the "F" in the data column for this reference returns the first page of this article to your browser (see the picture below). You can then either read the article online, print it, or even send it to your fax machine (within the United States only). Several resolutions are available, up to 600 dots per inch.

We have obtained permission from most astronomical publishers to scan their journals and make them available through the ADS. We currently offer the Astrophysical Journal (1988-95), the Astrophysical Journal Letters (1975-96), the Astronomical Journal (1975-95), Publications of the Astronomical Society of the Pacific (1975-95), Publications of the Astronomical Society of Australia (1975-93), Revista Mexicana de Astronomica y Astrofisica (1975-95), and Observatory Reports of Skalnate Pleso (1983-95). We are in the process of scanning the Astrophysical Journal back to 1975 as well as several other periodicals: Astronomy and Astrophysics, Monthly Notices of the Royal Astronomical Society, Bulletin of the Astronomical Society of India, Publications of the Astronomical Society of Japan, and Baltic Astronomy. We are negotiating with other publishers. To protect the journals' currency the scanned articles are available only after a certain lag time (six months to one year).

The journals are available directly through the address http://adsabs.harvard. edu/ads_article.html. Access by e-mail is also available.


The third major part of the ADS provides access to more than 200 astronomical catalogs. These catalogs include well-known classical ones such as the Yale Bright Star Catalog or the General Catalog of Variable Stars, as well as other more specialized ones like the All Sky Catalog of Extragalactic Radio Sources at 2.7 GHz or Optical Positions of 221 Radio Stars. Browsing these catalogs is more complex than using the abstract service since the search capabilities are broader. There is a "help" link on every page for assistance.

We can look more closely at this service by using our example of extrasolar planets. To begin their study the astronomers first had to decide which stars to examine. Ideally, the stars should be nearby and bright. A good place to start is the Yale Bright Star Catalog.

The "ADS Catalog Access Service" link on the Catalog Service page at brings up the main form (see next page). The top part allows you to select how to list the catalogs (by data center, by subject, or by name). You also need to specify how you want to query the database later on, either "query by table" (QBT) or "structured query language" (SQL). The bottom part of the form lets you search for catalogs by specifying words from the catalog description.

For our example we can get the list of catalogs by name and look for the Yale Bright Star Catalog (or put these words in the search field). The returned page displays a catalog list, with each entry featuring a button to call up the appropriate QBT or SQL form, a hyperlink to the catalog documentation, and a one-line description.

To begin a detailed search of the desired catalog, click on the "get" button to bring up the query form. The QBT form will allow you to specify search criteria for each field (column). It also allows you to reformat the data table if necessary (the default array generally produces the best results). Clicking on the catalog name provides complete documentation, with a detailed description of each column and the data formats. Links to the column titles offer information specific to that field. Click the checkbox next to each column you wish to retrieve, or mark the first box next to the catalog name to select all columns.

In our example I have selected the fields "Name," "v" (the magnitude), "Parallax" (inverse distance), and "cra" and "cdec" (coordinates in sexagesimal notation). In the parallax field I entered the search condition of [less than]0.1[inch] to restrain the search to stars closer than 10 par-secs. The search results include familiar names like Alpha Centauri and Sirius (Alpha Canis Majoris).

The SQL query form is more complex and requires detailed knowledge of both the SQL language and the particular database. It is useful only in very specialized applications.

The "Data type for return" option on both query forms lets you select the table or file output. Tables are displayed to the WWW browser; files are saved to disk.

While most of these catalogs are of specialized interest, amateurs may find the Minnesota APS POSS I catalogs of general interest. They contain data from the Automatic Plate Scanner (APS) processing of the Palomar Observatory Sky Survey (POSS) first-epoch (I), photographic O (blue), and E (red) plates. Besides offering object identifications and positions, when retrieving data from these catalogs you can also request finder charts displaying stars and galaxies. The map is returned in PostScript format, which can be sent directly to a PostScript-capable printer. This makes it easy to produce a detailed finder chart for your next night's observing. These catalogs currently do not have complete sky coverage, but the plate scanner is working continuously to add new areas.

The utility of the World Wide Web is growing at a phenomenal rate. With the help of the ADS, amateur astronomers with an Internet connection can now have free and easy access to the technical papers and catalogs of the professionals. For more information, visit our WWW site or send e-mail to ads@cfa.

GUNTHER EICHHORN Harvard-Smithsonian Center for Astrophysics 60 Garden St. Cambridge, MA 02138

Eichhorn is Project Scientist for the Astrophysics Data System project.

RELATED ARTICLE: Guide to Professional Resources

By Stuart J. Goldman

Periodically I am reminded that I belong to a minority; I'm a computer user who actually reads manuals (often before I even start using a new program). Sometimes I'll blunder through software without any documentation, but if it's a product I seriously intend to use (as opposed to a program I'm just curious about), I very much like to know what I'm doing. Thus, it is bothersome not to have a manual included with software but find instead an interactive help file. I would still rather sit with the book and mark important pages than have to hit the down arrow repeatedly on a help file's scroll bar (or be forced to use my own paper to print the file out).

As Gunther Eichhorn describes in his article (page 81), the Astrophysics Data System has documentation online. Other Internet resources have similar capabilities. Wouldn't it be nice if there were a book outlining all of them? To a degree, this is offered in Information & On-line Data in Astronomy edited by Daniel Egret and Miguel A. Albrecht (Kluwer Academic Publishers, 1995). Although intended for professional astronomers, amateurs may be interested in the contents. For example, the book has a chapter that describes the NASA/IPAC Extragalactic Database (NED), which is referenced, among other places, on the Digital Sky Survey (

However, as compelling as this 291-page book is, its price of $154.00 will likely quell any nonprofessional's enthusiasm for it. Academic publishers typically produce books for libraries and other institutions. At a more modest price, I'm sure this book would have a much greater appeal. It is an update of the similarly titled 1991 Databases & On-line Data in Astronomy, so if the publisher produces a third edition, perhaps it could be more reasonably priced for amateurs.

If you're still intrigued, you can find a complement to the book (not the complete text) on the World Wide Web at This site offers a description of the book's contents and features up-to-date changes in the book's text and Internet links.
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Title Annotation:Astrophysics Data System
Author:Eichhorn, Gunther
Publication:Sky & Telescope
Date:Oct 1, 1996
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